Thermoplastics are ubiquitous in modern life, being used for a myriad of purposes. Among these uses are packaging, mechanical parts, electrical and electronic apparatus parts, appliance parts, vehicle and automotive parts, toys, furniture, tanks, etc. In some cases, often for improved or distinctive appearance, and/or to match painted metal parts, the thermoplastic parts are painted (coated) using various types of paints (coatings). These paints may be applied in a number of conventional ways, for instance brush, spray or immersion coating.
One problem often encountered in painting thermoplastics is the (often poor) adhesion of the paint to the thermoplastic. Most paints are organic polymers, or form polymer upon curing, and the polymers used in the paints are usually different than the thermoplastic being coated. It is well known in the art that different types of polymers are usually incompatible with one another and often have poor adhesion to one another. Additives are often added to the paints to improve paint adhesion. However these additives sometimes adversely affect properties of the paint or cannot be used in specific cases where surfaces to be painted with the same coating are of different nature for example plastic surfaces side-by-side to metal surfaces as in automotive exteriors. It is therefore desired to develop a method to improve paint adhesion by modifying the thermoplastic composition, thus not adversely affecting other properties of the paint system.
A data sheet for “Dow Corning® 57 Additive”, which is reported to be a polyether modified siloxane states that it is a useful additive in coatings and paints to improve leveling, reduce coefficient of friction, mar resistance, and enhance gloss. Nothing is stated about improved adhesion to a substrate, nor about adding this material to a thermoplastic to improve adhesion of a paint.